The present invention is directed to a process for the preparation of a toner mixture using at least two toners which comprise at least a binder resin and optionally a coloring agent. Moreover, the present invention is directed to a developer composition comprising a mixture of at least two of said toners and optionally a carrier.
A process for preparing a colored toner blend is known from EP-B-0 614 128. According to the teaching of this document, the toners comprise a resin, pigment particles, an internal charge additive, and optionally surface additives. Moreover, each toner contains a blend compatibility component, selected from the group consisting of quaternary ammonium compounds, complexes of distearyl dimethyl ammonium methyl sulfate, organic sulfonates, trialkyl hydrogen ammonium bisulfates, potassium (3,5-di-t-butylsalicylato) borate, calcium salt of salicylatic-acid, tert-butyl salicylic acid complexes, aluminum salt complexes and zinc salt complexes. The surface additives may comprise metal salts of fatty acids, colloidal silica particles, metal oxides or mixtures thereof. It is particularly preferred that the surface additives comprise a mixture of metal salts of fatty acids and colloidal silica. In accordance with the examples, a specified commercially available silica and zinc stearate are used as the surface additives. Owing to the use of the blend compatibility components it is possible to obtain a rapid admixing time of the constituents. More specifically, the blend admix time can be reduced when compared with toner compositions which do not comprise any blend compatibility components.
U.S. Pat. No. 5,370,982 reveals a process for the preparation of colored toners which comprises providing a first toner comprised of resin, pigment particles, internal charge additive, and optional surface additives, adding thereto a second toner comprised of resin, pigment particles, internal charge additive, and optional surface additives, and wherein said toners contain external blend compatibility components.
However, the known toner compositions comprising said blend compatibility additives have disadvantages because they show a demixing phenomenon when they are used for printing or copying purposes. Moreover, it has been found that the color was not constant during a long period of use.
It is thus an object of the present invention to provide a process for the preparation of a toner mixture with improved characteristics so that no demixing occurs and wherein the triboelectric characteristics and, if the toner mixture is used within a two-component developer, the toner concentration and conductivity of toner and carrier components in the developer mixtures are not impaired during a prolonged use.
The present invention provides a process for the preparation of a toner mixture, preferably a colored toner mixture which comprises mixing a first toner with at least one further toner wherein the first toner has an acid value of 0.1 to 30 mgKOH/g and comprises at least one binder resin and at least one coloring agent wherein said binder resin comprises as the main component a polyester resin, and wherein the further toners comprise at least one binder resin and optionally at least one coloring agent. In contrast to the description of U.S. Pat. No. 5,370,962 it is not necessary to use an external blend compatibility component.
Moreover, the present invention provides a developer composition which comprises a mixture of the above mentioned at least two different toners and optionally a carrier.
According to the process it is possible to mix different toners with each other. One or more of these toners may comprise the coloring agent as an optional component, only. It is also possible to use a fluorescent toner and to mix it e.g. with a transparent toner which does not contain any coloring agent and/or further colored toners. It is particularly preferred that the binder resins of the different toners to be mixed are substantially identical. In such a case, the print qualities are excellent even during a long term of use.
Owing to the use of the specified toners it is surprisingly possible to prepare a toner mixture comprising at least two different toners so that a new color can be prepared without resulting in any de-mixing problem. It has been found that no de-mixing of the individual toners occurs even if the toner mixture is repeatedly used. In this regard, the applicants performed experiments in which toner mixtures were used for printing. With each toner mixture 1,000 to up to 200,000 prints have been performed, and no de-mixing tendency could be recognized.
The developer composition, prepared from a specific toner mixture, has an excellent performance. More specifically, the triboelectric characteristics, the toner concentrations and the conductivity of carrier and developer remain unchanged. More specifically, these values approximately correspond to the respective average values of each of the single toners used for preparing said toner mixture. Moreover, also the print quality and especially the background behavior of the toner mixture corresponds to that of the individual toners. Hence, this developer composition may be used for printing or copying purposes.
By mixing at least two different toners with each other it is possible to obtain a plurality of new colours. Hence, the preparation of a wide range of different colours by mixing the individual toners is possible.
It is possible to mix more than two toners with each other. There is no restriction with respect to the mixing ratio of the two or more toners.
The toners have an acid value within the above range. Preferably, the acid value is within the range of 0,1 to 25 mgKOH/g, most preferably 5 to 25 mgKOH/g. The acid value is measured in accordance with JIS K0070 and ASTM D1980-67. If the acid value falls within the ranges as defined herein, especially a good dispersibility of the coloring agents may be obtained, thereby reducing the tribo effect of the coloring agent. Therefore the triboelectric properties of each of the loners are predominantly due to the resin and optional charge control agents and hence the triboelectric characteristics remain stable in the toner mixture.
The binder resin of the first toner and optionally of the further toners comprise a polyester as the main component. It is particularly preferable to use polyesters having similar triboelectrical behavior. Then, the mixing is excellent, and the hue and chroma of the resulting colour do not change during repeated use. The acid value of the binder is not restricted to the range of the acid value of the toner as mentioned above. It may be much higher, e.g. up to approximately 45 mgKOH/g provided that the toner has an acid value falling within the above-mentioned range.
The average (by volume) particle size of the toner particles to be blended is preferably 3 to 20 xcexcm, more preferably 5 to 15 xcexcm, as measured by Coulter Multisizer with 100 xcexcm aperture.
The pigment of the coloring agent may comprise yellow, magenta, cyan, black, red, green, blue, orange, white, gray fluorescent, metallic or metallic effect particles or mixtures thereof. Particles having a metallic effect are commercially available, e.g. under the tradename Iriodine (Merck GmbH) As stated above, it is possible to use a transparent toner which does not contain any coloring agent and to mix the same with at least one further toner which contains a coloring agent.
The amount of the coloring agent in a colored toner is preferably 1% to 25% by weight, based on the total weight of each of the individual toner compositions. More preferably, the amount of the coloring agent is 1% to 10% by weight, based on the toner composition. If a fluorescent toner is used, its fluorescent additive is normally used in a small amount, preferably 0,1% to 1% by weight, because it is highly effective.
The toner mixture may additionally comprise an internal charge controlling agent. The internal charge controlling agent may be a single compound or may be composed of a mixture of different charge controlling agents. The selection of a charge controlling agent depends on whether a positively chargeable toner or a negatively chargeable toner is used.
Examples of a positively chargeable toner include quaternary ammonium salt compounds such as xe2x80x9cTP-415xe2x80x9d (Hodogaya Chemical Co., Ltd.), xe2x80x9cTP-302xe2x80x9d (Hodogaya Chemical Co., Ltd.), xe2x80x9cTP-4040xe2x80x9d (Hodogaya Chemical Co., Ltd.), xe2x80x9cBontron P-51xe2x80x9d (Orient Chemical Co., Ltd.) and xe2x80x9cCopy Charge PSYxe2x80x9d (Clariant GmbH); polyamine resins such as xe2x80x9cAFP-Bxe2x80x9d (Orient Chemical Co., Ltd.); polymer functionalized with quaternary ammonium salt such as xe2x80x9cFCA-201-PSxe2x80x9d (Fujikura Kasei Co., Ltd.); and with a preference given to TP-415, TP-302 and Bontron P-51.
Examples of a negatively chargeable toner include potassium borobisbenzylate such as xe2x80x9cLR-147xe2x80x9d (Japan Carlit Co., Ltd.); metal complexes of alkyl derivatives of salicyclic acid such as xe2x80x9cBontron E-81xe2x80x9d (Orient Chemical Co., Ltd.), xe2x80x9cBontron E-84xe2x80x9d (Orient Chemical Co., Ltd.) and xe2x80x9cTN-105xe2x80x9d (Hodogaya Chemical Co., Ltd.); Calixarene compounds such as xe2x80x9cBontron E-89xe2x80x9d (Orient Chemical Co., Ltd.) and xe2x80x9cBontron F-21xe2x80x9d (Orient Chemical Co:, Ltd.); and polymer functionalized with sulfonic acid such as; xe2x80x9cFCA-1001-NSxe2x80x9d (Fujikura Kasei Co., Ltd.), quaternary ammonium salt compounds such as xe2x80x9cCopy Charge NX VP434xe2x80x9d (Clariant GmbH), and with a preference given to LR-147, Bontron E-81, and Bontron E-84.
This charge controlling agent is preferably used in an amount of approximately 0,5% to 5% by weight, based on the total amount of each of the toner compositions. Particular preferably, the amount thereof is approximately 1% to 2% by weight.
Optionally, the toner particles may further comprise a wax component which is commonly used in toner compositions. It is preferred to use low molecular weight waxes such as polyolefins which are commercially available. Out of these commercially available polyolefins, polyethylenes and polypropylenes are preferably used. The wax materials are contained in the toner composition in an amount of from about 1% to 10% by weight, based on the total amount of each toner. It is particularly preferred to use such a wax compound in an amount of 1% to 5% by weight.
As a surface additive of each of the toner particles, silica may be used. The silica is a preferably colloidal silica and is commercially available such as Aerosil R-972. This silica is generally present in an amount of from 0,1% to 5% by weight, preferably 0,1% to 1% by weight.
The developer composition of the present invention may comprise in addition to the toner mixture as described above, a carrier. Any carrier generally employed may be used even though it is preferred to use a carrier having a rugged surface. More preferably a porous carrier is used. It is particularly preferred to use a carrier having a large specific surface area because this leads to advantageous effects with respect to the triboelectricity. A particularly preferred carrier includes an iron powder coated with resins. The iron particles preferably have an irregular shape. The carrier preferably has a resistivity of from 7 to 12 log xcexa9, more preferably 8 to 10 log xcexa9, as measured by C-Meter of Epping GmbH.
It is preferred that the difference of the apparent densities of the toner particles contained in said toner mixture is 0,1 g/cm3or less, more preferably 0,05 g/cm3 or less.
The toner mixtures prepared in accordance with the process of the present invention may be used in electrographic (which includes electrophotographic, electrostatic, ionographic (e.g. Delphaxf-machines), magnetographic (Nipson process)) imaging and printing operators. These can also be used for colour xerography.
The invention is especially advantageous for the preparation of custom colors individually designed for company logos like Ocxc3xa8/red, Siemens/green or Exxon/red. So far, it has been difficult to meet these colors by electrographic processes. Therefore, it is common to use re-processed paper with company logos printed by off-set printers and print the necessary digital information e.g. in black on the re-printed paper by high speed electrographic engines later on.
It has been shown that the invention can be used in a highly advantageous way in electrographic printers having two print stations as described more specifically in U.S. Pat. No. 5,546,178 (Manzer) application Ser. No. 428,170, or U.S. Pat. No. 5,659,875 (Hausmann), application Ser. No. 621,163, hereby incorporated into the specification by reference. Those printers comprise a first printing station for printing a first color and a second printing station for printing a second color (e.g. spot color process) on the same front or reverse page. Associated with both printing stations are respective developer stations with respective colored toner in there. By using standard toner of any color, preferably black, in the first printing station, to print text information and toner mixtures according to the invention in the second printing station for printing e.g. company logos or spot color information on the same page, the costly usage of paper re-printed by off-set engines can be avoided and the whole print job can be done merely by that two engines electrographic printer.
Instead of using a printer with two engines, electrographic printers coupled in tandem as described in U.S. Pat. No. 4,609,279 (Hausmann), application Ser. No. 703,915 can also be used.
The developer compositions preferably have a triboelectric charge of from about 5 to 50 xcexcC/g, more preferably 10 to 40 xcexcC/g, especially 15-25 xcexcC/g. Such a range of the triboelectric charge leads to a good transfer of the toner mixture to a paper support. It is also preferred that the difference of the triboelectric charges of the toners to be mixed is at most 20, more preferably at most 10 xcexcC/g. The triboelectric charge is measured by using a Q/M-Meter device, manufactured by Epping GmbH, Germany. The concentration of the toner mixture in the developer composition is preferably 1 to 10% by weight, more preferably 3 to 7% by weight.
In the following, the present invention is described in greater detail by way of examples. Parts and percentages are by weight unless otherwise indicated.